Despite recent advances in therapy, far too many youth and young adults (YYAs) with type 1 diabetes (T1D) and type 2 diabetes (T2D), particularly those of minority race/ethnicity, do not achieve optimal glycemic control thus placing them at increased risk of acute and chronic complications. Among the social determinants of health, household food insecurity (HFI) may be a key barrier to achieving glycemic control and may lead to increased health care utilization and costs, but virtually all of the limited research was cross-sectional and conducted in older adults with T2D. Moreover, racial/ethnic minorities are disproportionately affected by HFI, which may underlie similar disparities in diabetes outcomes. Our preliminary work suggests that HFI is a common phenomenon in YYAs with diabetes, affecting 19% of YYAs with T1D and 38% of those with T2D. These rates significantly exceed the 2015 national estimate of 12.7%. We propose a longitudinal study, the SEARCH Food Security (SFS) cohort study, which is designed as an ancillary study to the ongoing CDC/DDT- and NIH/NIDDK-funded SEARCH for Diabetes in Youth 4 study, a racially/ethnically diverse study of diabetes diagnosed in youth. The aims of the SFS study are to: (1) Initiate a food insecurity cohort study of 1,187 YYAs aged 15-35 years (53% minority) with T1D and T2D by adding two data collection time points to the ongoing SEARCH 4 study; (2) Prospectively evaluate the influence of HFI on changes in glycemic control in YYAs with T1D and T2D; (3) Quantify the mediating role of nutritional, mental health, and behavioral pathways through which food insecurity may affect changes in glycemic control in YYAs with T1D and T2D; and (4) Prospectively evaluate the influence of HFI on changes in health care utilization and medical and non-medical health care costs in YYAs with T1D and T2D. Using the SFS data in tandem with extensive data collected by SEARCH will be highly efficient for addressing these aims. The proposed study will be the first cohort study to examine the impact of food insecurity on glycemic control, health care utilization, and costs among a diverse population of US YYAs with T1D and T2D. Our transdisciplinary team is led by Drs. Liese and Mendoza, recognized experts in diabetes, epidemiology, pediatric medicine, disparities, and food insecurity research, and is supported by a team comprising expertise in pediatric endocrinology, psychology, health behaviors, health economics, biostatistics, and causal inference modeling. The study has the potential to alter diabetes policy and clinical practice by establishing the need for more in-depth assessments of food insecurity among YYAs with diabetes, re-assessment of diabetes management and nutrition recommendations for food-insecure patients, and integration of food assistance resources into routine care for persons with diabetes. It will also inform the tailoring of interventions to address food insecurity, especially for minorities, in future diabetes research trials.